A casing is cemented within a well bore (P) or pipe by means of a radially expandable tubular preform (1). For this purpose, a) the folded preform (1) is inserted into the well (P) or pipe down to the required level; b) the well is sealed off at the bottom of the preform (1) by means of an inflatable hydraulic retainer (4); c) a curable fluid cement is injected onto the retainer so that it surrounds the lower portion of the preform; d) the preform is gradually unfolded from the top towards the bottom to press the cement against the wall of the well or pipe along the full length of the preform; e) the preform is cured to form a casing while the cement is allowed to set; and f) the retainer (4) is deflated and withdrawn from the well or pipe.
